Assembly and processing of an engineered amelogenin proteolytic product (rP148)

The purpose of this study was to express, characterize, and investigate the self-assembly of a recombinant porcine amelogenin lacking the hydrophilic 24 C-terminal amino acids (rP148). To gain further insight into the function of amelogenin processing during enamel mineralization, this protein was also used as a substrate to examine the action of matrix metalloproteinase-20 (MMP-20). The assembly properties of rP148 were monitored by dynamic light scattering (DLS). In general, rP148 molecules assemble into monomers, dimers, oligomers, and some nanosphere-like particles. Depending on the solution conditions, large aggregates were also observed. Matrix metalloproteinase-20 cleaved the rP148 molecule at a few sites, creating a number of different products, including the tyrosine-rich amelogenin polypeptide (TRAP). Our data suggest that although rP148 self-assembles into small particles, its assembly properties are different from those of the full-length rP172, indicating that the C-terminal 24 amino acids play a critical role in nanosphere assembly. We further demonstrate that MMP-20 digests rP148 in a manner that generates a similar proteolytic pattern, as would be expected to occur in vivo.